Pneumatic springs which are designed as rolling bellows are, in terms of their basic construction, composed of a rolling piston to which the one end of a rolling bellows is fastened. The other end of the rolling bellows adjoins a closure cover or a second rolling piston. The rolling pistons are very differently equipped. To achieve a high level of spring comfort, it is expedient for the internal volume of the rolling piston to also be utilized for the spring action. The rolling piston is then designed as a hollow body and is generally assembled from multiple parts. Such designs are cumbersome and correspondingly expensive. Normally, the rolling pistons are assembled from two parts which are welded together. In the case of two-part steel pistons, the weld seam has approximately the same strength as the base material. It is more problematic if the rolling piston is produced from plastic. In the case of a two-part rolling piston composed of a plastic, this results in restrictions in terms of function. For strength reasons, it is normally not possible for the entire spring travel to be utilized. Rolling pistons composed of plastic for utility vehicles may duly also be produced in unipartite form, but have a small internal volume, which leads to reduced comfort of the pneumatic spring.
WO 2007/142153 A1 presents a pneumatic spring which has a two-part piston. The piston is composed of an upper part and a lower part which are welded together. On the upper part of the piston there is provided an inwardly directed shoulder onto which the bead-like plug-on edges of the rolling bellows are plugged. The other end of the rolling bellows has specially formed edges which are encompassed by a flanged edge of a cover. The interior space of the piston is permanently connected to the interior air chamber of the rolling bellows. A disadvantage of this embodiment is the two-part design of the rolling piston and the different design of the fastening ends of the rolling bellows.
A similar design to that described above emerges from the U.S. Pat. No. 6,386,524 B1. In said document there is provided a piston embodiment in which the piston is produced from plastic and has a double annular wall which is closed off by a base. Also provided in said document is a two-part design of the rolling piston and a rolling bellows which is equipped with different plug-on edges.
A further embodiment of a rolling piston composed of plastic is presented in DE 10 2006 040 546 B4. In said document, there is likewise provided a piston which has an inner and an outer chamber which communicate with one another via openings. Also, in said document, the piston is closed off by a cover, such that a two-part embodiment is provided.
Further two-part embodiments of plastics pistons emerge from WO 2009/015821 A1 and EP 1 862 335 B1.
In U.S. Pat. No. 3,078,086 an air spring with a rolling piston in a unipartite form is disclosed, at which inner side a bead of a rolling bellows is fastened by a cup.
WO 02/035112 A1 shows an air spring, which air spring bellows is fastened at the inner side of a rolling piston by means of a fastening ring. The inner side of the rolling piston and the fastening ring thereby form corresponding conical surfaces.
Further EP 0859 165 A1 discloses an air spring with a hose rolling bellows, providing a sealing bead with a metallic core, wherein the sealing bead is fastened at the outer side of a rolling piston.